move install to Makefile; add install for man

Makefile

@@ -21,6 +21,17 @@ build: build/ build/$(NAME)
 build/$(NAME): src/main.c $(HEADERS)
 	cc -o $@ $<
 
+define PREFIX
+ifeq $(UID) 0
+	/usr/local
+else
+	$(HOME)/.local
+endif
+endef
+
+install:
+	install -CDm0755 -t $(PREFIX)/bin/ build/$(NAME)
+	install -CDm0644 -t  $(PREFIX)/share/man/man1 build/$(NAME)
 
 test:
 	$(error testing using `make' not supported; use `just')